1. Field of the Invention
The present invention relates to a machine tool with a main body covered with a cover of a type such that air inside the cover is sucked in by a mist collector.
2. Description of the Related Art
In order to increase the productivity of machine tools, their spindles are being improved for higher-speed rotations and higher outputs. To attain this, a cutting fluid is generally jetted onto a tool and a machining area of a workpiece, thereby cooling the tool. In the machine tool in machining operation, the cutting fluid is repelled and scattered as a mist by the tool that is rotating at high speed. A main body of the machine tool is covered with a cover in order to prevent the mist from being scattered to the outside of the machine tool. Further, the misty cutting fluid that is caught inside the cover is sucked in and recovered together with air in the machine tool by means of a mist collector that is connected to the cover. Here, “main body” of a machine tool means all constituent elements of the machine tool with a cover excluded.
Referring now to the top view of FIG. 4 and the side view of FIG. 5, there will be described a prior art example of the machine tool, in which the main body of the machine tool is covered with the cover and the misty cutting fluid is sucked in and recovered together with air from a sealed space inside the cover by means of the mist collector.
A cover 1 is disposed on a base 10 of the machine tool so as to enclose the main body of the machine tool and cut off and seal the interior (machining area) of the machine tool from the outside. The cover 1 covers a spindle head 3, spindle 4, tool 5, table 6, etc. of the machine tool. The spindle head 3 is driven in a vertical direction (Z-axis direction) by a Z-axis motor Mz. The spindle 4 is rotatably mounted on the distal end of the spindle head 3 and is rotated by a spindle motor Ms that is mounted on the spindle head 3. The table 6 is driven in an X-axis direction perpendicular to the Z-axis direction by an X-axis motor (not shown). The table 6 is also driven in a Y-axis direction perpendicular to the X- and Z-axis directions by a Y-axis motor My. In FIGS. 4 and 5, numerals 1a and 1b denote a ceiling portion of the cover 1 and a door of the cover 1 in front of the machine tool, respectively, and numeral 9 denotes a handle of the door 1b. 
A workpiece (not shown) is mounted on the table 6, while the tool 5 is mounted on the distal end of the spindle 4. A cutting fluid is jetted onto the tool 5 and the machining area of the workpiece through a cutting fluid supply pipe 11 as the spindle motor Ms is driven to rotate the spindle 4 and the tool 5. Further, X-, Y-, and Z-axis motors Mx, My and Mz as feed axis motors are drivingly controlled to enable the tool 5 to machine the workpiece. The fed cutting fluid is discharged from the machine tool through a trough 12 at its lower part and recovered.
Since the spindle 4 and the tool 5 rotate at high speed, the fed cutting fluid is repelled and scattered as a mist into the space inside the cover 1. The scattered cutting fluid is sucked in and recovered together with air through a suction pipe 7, which internally connects with the cover 1 and is located at an upper part of the machine tool, by the mist collector 2. The outside air flows into the space inside the cover through a clearance of the cover 1 that covers the main body of the machine tool. Since a space for the communication between the space inside the cover and the outside is particularly wide at a cutting fluid outlet portion of the trough 12 at the lower part of the machine tool, however, the outlet portion of the trough 12 forms a main inlet passage for the outside air that flows into the space inside the cover, as indicated by arrow A in FIG. 5.
Since the mist collector 2 sucks in the air from the space inside the cover, air flows into the inside space mainly through the cutting fluid outlet portion of the trough 12 at the lower part of the machine tool, as indicated by arrow A, and passes through the space inside the cover 1, as indicated by arrow C. Then, the air is sucked into the mist collector 2 through the suction pipe 7, as indicated by arrow D. Thus, the resulting misty cutting fluid is sucked in and recovered together with the air by the mist collector 2.
In the conventional machine tool, as described above, its main body is covered with the cover to prevent the misty cutting fluid from being scattered out into the space in which the machine tool is installed and polluting the environment. Further, the misty cutting fluid is sucked in and recovered together with the air from the space inside the cover by means of the mist collector that internally connects with the cover.
If the main body of the machine tool is covered with the cover, on the other hand, the temperature inside the cover is increased by heating of the motors. Since a temperature change exerts a bad influence on the machining accuracy, the temperature inside the cover must be prevented from increasing. A technique to attain this is described in Japanese Patent Application Laid-Open No. 2002-200539 such that an increase in temperature inside a cover is prevented by locating feed axis motors, such as X-, Y- and Z-axis motors, outside the cover.
Heat generating sources in the machine tool mainly include the machining area between the tool and the workpiece, the feed axis motors, i.e., the X-, Y- and Z-axis motors, and the spindle motor.
According to the aforesaid system of Japanese Patent Application Laid-Open No. 2002-200539, a temperature increase inside the cover is prevented by locating the X-, Y- and Z-axis motors outside the space that is covered with the cover. Since the spindle motor is mounted on the spindle head in order to drive the spindle to which the tool is attached, however, it is located in the space inside the cover. Since the spindle motor rotates the spindle and the tool at high speed, moreover, it generates more heat than the X-, Y- and Z-axis motors. Furthermore, the spindle motor is provided with a built-in fan for cooling the spindle motor at the rear part thereof. Air is sucked in from the distal end side of the spindle motor through vents formed in the outer periphery of the motor, and exhaust air is discharged to the rear side of the motor.
If the spindle motor constructed in this manner is located in the space inside the cover, therefore, the air inside the cover that is warmed by heat generated by the rotation of the spindle motor is sucked in by the built-in fan of the spindle motor and fed into the vents in the outer periphery of the motor. Thus, the cooling effect of the fan for the spindle motor is reduced inevitably.
Since the built-in fan of the spindle motor sucks in the air that contains the mist in the machine tool, moreover, the mist containing sludge that is produced by machining adheres to and locks the fan, thereby lowering the reliability of the system.